In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. A resist material in which the exposed portions of the resist film become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions of the resist film become insoluble in a developing solution is called a negative-type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization. Typically, these miniaturization techniques involve shortening the wavelength (increasing the energy) of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production of the semiconductor elements. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a wavelength shorter (energy higher) than these excimer lasers, such as electron beam (EB), extreme ultraviolet radiation (EUV), and X ray.
Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources.
As a resist material that satisfies these conditions, a chemically amplified composition is used, which includes a base material component that exhibits a changed solubility in a developing solution under the action of acid and an acid generator component that generates acid upon exposure.
For example, in the case where the developing solution is an alkali developing solution (alkali developing process), a chemically amplified positive resist which contains, as a base component (base resin), a resin which exhibits increased solubility in an alkali developing solution under action of acid, and an acid generator is typically used. If the resist film formed using the resist composition is selectively exposed during formation of a resist pattern, then within the exposed portions, acid is generated from the acid generator component, and the action of this acid causes an increase in the polarity of the base resin, making the exposed portions soluble in the alkali developing solution. Thus, by conducting alkali developing, the unexposed portions remain to form a positive resist pattern.
On the other hand, in a case where such a base resin is applied to a solvent developing process using a developing solution containing an organic solvent (organic developing solution), when the polarity of the base resin is increased, the solubility of the exposed portions in an organic developing solution is relatively decreased. As a result, the unexposed portions of the resist film are dissolved and removed by the organic developing solution, and a negative resist pattern in which the exposed portions are remaining is formed. Such a solvent developing process for forming a negative-tone resist composition is sometimes referred to as “negative-tone developing process” (for example, see Patent Document 1).
In general, the base resin for a chemically amplified resist composition contains a plurality of structural units for improving lithography properties and the like. For example, in the case of a resin composition which exhibits increased solubility in an alkali developing solution by the action of acid, a structural unit containing an acid decomposable group which is decomposed by the action of acid generated from an acid generator component and exhibits increased polarity is used. Further, a structural unit containing a lactone-containing cyclic group or a structural unit containing a polar group such as a hydroxy group is used (for example, see Patent Document 2).
On the other hand, as acid generators usable in a chemically amplified resist composition, various types have been proposed including, for example, onium salt acid generators; oxime sulfonate acid generators; diazomethane acid generators; nitrobenzylsulfonate acid generators; iminosulfonate acid generators; and disulfone acid generators.
Further, as the miniaturization of patterns proceeds, a chemically amplified resist composition further containing an acid diffusion control agent, for obtaining an excellent contrast and for preventing roughness of a resist pattern and pattern collapse, as well as a base component and an acid generator component.
Patent Document 3 discloses a radiation-sensitive resin composition containing a compound which has a characteristic that, at unexposed portions of the resist film, an ion-exchange reaction with acid generated from an acid generator component and the like upon exposure is caused, thereby preventing diffusion of acid; and at exposed portions of the resist film, the compound is decomposed thereby, losing the basicity thereof with respect to acid generated from an acid generator component and the like.